As, for example, DE 607 273 A discloses, it is known that components of a two-stage or multiple-stage steam turbine have to be heated up before the operation of the steam turbine or have to be kept hot in an intermediate mode of the steam turbine, in order to avoid damage of the steam turbine. Utilization of heating-up and keeping-warm concepts which are provided for this purpose makes short start-up times possible of a power plant which comprises a steam turbine, which is associated with enormous advantages for plant constructors and plant operators.
Components of a steam turbine can be kept warm by feeding externally generated steam, for example auxiliary steam, sealing steam or the like, to the components of the steam turbine. Typical temperatures of the steam which is used here can be from approximately 250° C. to approximately 300° C. The steam can be introduced, for example, into a middle pressure stage of a multiple-stage steam turbine, it being possible for the steam to expand in the direction of a low pressure stage of the steam turbine, which low pressure stage is connected downstream of the middle pressure stage.
The components of a low pressure stage of a steam turbine are usually not designed for outflow temperatures of 300° C. Therefore, in the case of an introduction of steam which is used for heating up a steam turbine or keeping a steam turbine hot into the low pressure stage, significant limitations can be produced for the components of the low pressure stage which can shorten the service life of the low pressure stage substantially. In order to avoid this, the components of a low pressure stage can be cooled during heating up of a steam turbine or keeping a steam turbine hot, for example by means of water injection (what is known as housing spraying) and/or by means of two-phase injection. However, this is associated with additional costs for the cooling.